VSAT TECHNOLOGY – COMPLETE GUIDE
A Very Small Aperture Terminal (VSAT) is a device known as a small private earth station that is used to transmit & receive data signals through a satellite.
Since the microwaves travel in straight lines, if the towers are too far away then the earth gets in the way. For communicating at a far distance high towers are needed which may be very expensive. Bands above 8 GHz are absorbed by water. Due to all these reasons satellite communication is preferred. VSAT is also one of the satellite communication systems used onboard ships.
VSAT network mainly uses GEO satellites in Ku, Extended-C , Ka band for their application purposes. Detail explanation of these bands are given in table below
| BAND | UP-LINK (GHz) | DOWN-LINK (GHz) | ISSUES |
| L | 1-2 | 1-2 | Small bandwidth |
| C | 5.925-6.425 | 3.7-4.2 | Interference with ground links, Large antenna size. |
| Extended-C | 6.725-7.025 | 4.500-4.800 | Weak signals, Large antenna size. |
| Ku | 14.0-14.5 | 11.7-12.2 | Attenuation due to rain. |
| Ka | 27.5-30.5 | 17.7-21.7 | High equipment cost. |
COMPONENTS
VSAT system is very simple it cansist of 3 main components
- Antenna Unit
- Control Unit
- Modem
The antenna unit provides the satellite link between the onboard modem and the land-based hub. Using its integrated GPS, advanced reflector technology, and gyro stabilization, the antenna automatically locates and tracks the correct satellite, even while your vessel is on the move. In addition, the antenna three-axis range of motion allows it to track the satellite at high elevations, even directly overhead (requires external NMEA true heading input).
The control unit links the antenna to the modem and allows you to operate and configure all aspects of the system.
The modem is the transceiver and brain of the system. It processes all incoming and outgoing TCP/IP data between the antenna and the switch using its proprietary spread spectrum technologies.
WORKING
Ku-band communications satellites are located in fixed positions above the Earth equator and relay data to/from the earth within the regions that they serve. Therefore, to communicate via a given satellite, you must be located within that satellite’s unique coverage area, also known as its footprint.
In addition, since satellites are located 22,300 miles (35,900 km) above the equator, the VSAT antenna must have a clear view of the sky to transmit and receive signals. Anything that stands between the antenna and the satellite can block signals, resulting in lost data.
NOTE: Common causes of blockage include trees, buildings, and bridges. Heavy rain, ice, or snow may also temporarily interrupt reception.
Signals are received at Antenna unit and antenna position automatically sets to satellite position by the help integrated GPS and Gyro feedback so that it continuosly tracks position of satellite regardless of position of ship to provide unterrupted signal reception & transmission.
The Control unit receives/transmits and modulates/demodulates the signal. It is an intermediate device between the Antenna Unit and modem. It also gets NMEA feed from Gyro helped to track the exact position of the satellite
The MODEM receives/transmits IP addresses from the various devices like routers, telephone, fax, etc transmits/receives IP address to the Control unit. providing an exchange of digital information. MODEM uses TCP/IP protocol access information from various sources across the world.
VSAT (VERY SMALL APERTURE TERMINAL) v/s FBB (FLEET BROADBAND)
| specs | VSAT | FBB |
| Technology | DSL network services | Mobile communication |
| Cost | Rate are fixed | Rate on Usage |
| Activation | Activation is through Satellite Router | Activation is through SIM card |
| Data Speed | Max 1 to 20Mbps | Max 432Kbps |
| Frequency Band | Ku | L |
| Coverage | Only main areas | Covers Globally |
VSAT system offers good internet speed but minimal coverage area compared to FBB. VSAT system is user friendly all realtime status can be monitored using a web user interface as shown in the below figure, that can be accessed onboard ship by entering the IP address given by maker in your browser application. You can also see the status, configure, control antenna & control unit remotely using any PC connected to the Ships LAN network.
Looking at Error Codes in VSAT Control Unit you can easily identify the type of fault.
Missed out something? write us mail@marineeto.we.bs
REFERENCE
- KVH www.kvh.com
- MARINE SATELLITE www.marinesatellitesystems.com
- SAFECOMNET www.safecomnet.com
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